1. Field of the Invention
The present invention relates to a grommet for mounting on a wire harness to be wired in automobiles, and a method of forming the grommet.
2. Description of Related Art
It is known in the art to mount a grommet on a wire harness wired from an engine compartment to a passenger compartment of an automobile. Such a grommet is mounted to an aperture of a car body panel that separates a passenger compartment from an engine compartment of the automobile. The grommet protects the wire harness passing through the aperture and provides protection from water and dust, as well as sound insulation between the engine compartment and the passenger compartment.
Several grommets of this general type are known in the art. An example of such a grommet is described in Japanese Patent Laid-open Publication 2004-187357 and shown in FIGS. 6A and 6B of the present application. The grommet 1 shown in FIGS. 6A and 6B includes a tubular or funnel shaped portion 2 having a gradually widening diameter and a tubular portion 3 linked to the smaller diameter end part of the funnel shaped portion 2. A body latch groove portion 4 is provided in the larger diameter end part of the funnel shaped portion 2, and fixes the grommet to a car body panel. An extended tubular portion 5 projecting from the tubular portion 3, which extends inside the funnel shaped portion 2, is provided. Anti-turn-up ribs 6 are arranged at 90 degree intervals, extending from the external circumferential surface of the extended tubular portion 5. A plurality of rib portions 2a are provided on the external surface of the funnel shaped portion 2. These rib portions 2a extend and radiate from the body latch groove portion 4 to the part of the funnel shaped portion 2 where the funnel shaped portion 2 joins the tubular portion 3. The wire harness W/H passes through the tubular portion 3 into the space inside the funnel shaped portion 2 of the grommet 1. The wire harness W/H is then fixed by a tape T at the end section of the tubular portion 3.
A wire harness W/H filled with a water sealing agent is passed through and tightly attached to the extended tubular portion 5, which extends inside the funnel shaped portion 2. Thereby, the wire harness has the function of a water sealing portion. Accordingly, having the extended tubular portion projecting into the funnel shaped portion, which surrounds the water sealing portion, enables the tubular portion extending from the funnel shaped portion to flex easily along with the wire harness. Flexibility in wiring and routing is thus improved. Further, reinforcing the extended tubular portion with the anti-turn-up rib prevents the extended tubular portion from turning up, and the sealing between the extended tubular portion and the wire harness is substantially kept intact. Further, the anti-turn-up rib is reinforced by being linked to the funnel shaped portion, deformation of the funnel shaped portion is thus avoided, and deformation of the body latch groove portion on the external circumferential surface can be prevented. Thereby, the gripping force attaching the grommet to the car body panel is further improved.
The grommet shown in FIGS. 6A and 6B has the above mentioned various advantages by providing an extended tubular portion that extends inside the funnel shaped portion, along with providing anti-turn-up ribs that extend and radiate on the external circumferential surface, the ribs being linked to the internal surface of the funnel shaped portion. As shown in FIG. 7, however, a problem arises when a wire harness is passed through the grommet 1. Specifically, when a wire harness is inserted into the grommet 1, expander fingers 101 of an expander 100 are placed inside the grommet 1, and then gradually expanded therein. The wire harness is inserted in a condition where the tubular portion 3 and the extended tubular portion 5 of the grommet 1 are expanded.
Expanding the diameter of the grommet using the expander fingers is difficult since the extended tubular portion 5 and the funnel shaped portion 2 are linked by ribs 6. Thus, it is difficult to expand the grommet to the required size.
The above stated problem can be solved by disconnecting a linking portion of the extended tubular portion 5 and the rib 6, or a linking portion of the rib 6 and the funnel shaped portion 2. However, without linking the rib 6 and the funnel shaped portion 2, deformation of the funnel shaped portion 2 cannot be controlled, which leads to a decrease of the gripping force when the grommet is attached to the car body panel. Further, when the linking portion between the rib 6 and the extended tubular portion 5 is eliminated, reinforcement for the extended tubular portion becomes insufficient, which causes the following problems: the extended tubular portion may be turned up easily and the water sealing function deteriorates. Therefore, as shown in FIG. 8, providing a notch 7 to the linking portion between the rib 6 and the extended portion 5 to reduce the size of the linking portion is considered.
However, when the rib 6 is configured as shown in FIG. 8, a problem arises: when the grommet 1 is formed, its removal from a metal mold becomes difficult. Specifically, as shown in FIG. 9, the grommet 1 is formed by using a metal mold 100 including an upper mold 101, a center mold 102, a lower mold 103 and a center core 104. The grommet is formed by filling the grommet forming material made of rubber or elastomer in the metal mold 100. Then, the upper, center, lower molds 101 through 103 are removed. Next, air is injected between the center core 104 and the grommet 1 using an air gun 120 so that the grommet 1 is expanded, and then the expanded grommet 1 is removed from the center core 104. In the process of the grommet 1 removal, air injected by the air gun 120 flows into the extended tubular portion 5, however, the air is not supplied between the center core 104 and a funnel shaped portion 2 of the grommet 1. As a result, the funnel shaped portion 2 of the grommet 1 cannot be sufficiently expanded, therefore, the grommet 1 cannot be removed from the center core 104.